Cooled electronic system

ABSTRACT

A sealable module, cooled electronic system and method are described relating to cooling a heat generating electronic device. The sealable module is adapted to be filled with a first cooling liquid and a heat transfer device having a conduction surface defines a channel for receiving a second cooling liquid. In one embodiment, at least a portion of the conduction surface or housing is shaped in conformity with the shape of the electronic component. Control of the second cooling liquid is also described. Transferring heat between the second cooling liquid and a third cooling liquid features in embodiments. A method of filling a container with a cooling liquid is further detailed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/778,049, filed May 11, 2010, which claims priority from U.S.Provisional Patent Application No. 61/177,548, entitled “CooledElectronic System,” filed on May 12, 2009, the disclosure of each ofwhich is hereby incorporated by reference in its entirety.

TECHNICAL FIELD OF THE INVENTION

This invention relates to a module or capsule for housing an electroniccomponent that generates heat in operation, a method of cooling such anelectronic component, a method of cooling an electronic device, a cooledelectronic system, and a method of filling a container for an electronicdevice with a cooling liquid. The invention is particularly applicable,for example, to computer processors and motherboards.

BACKGROUND OF THE INVENTION

Electronic components and in particular computer processors generateheat in operation, which can lead to overheating and consequent damageto the component and other parts of the system. It is thereforedesirable to cool the component to transfer the heat away from thecomponent and maintain the component temperature below the maximumoperating temperature that is specified for correct and reliableoperation of the component.

This issue especially concerns data processing or computer servercentres, where a substantial number of computer processors areco-located and intended for reliable, continuous operation over a longtime period. These centres may typically contain many server units,occupying multiple equipment racks and filling one or more rooms. Eachserver unit contains one or more server board. A single server board candissipate many hundreds of watts of electrical power as heat. Inexisting systems, the energy required to transfer heat continuously soas to maintain correct operation can be of the same order of magnitudeas the energy required to operate the servers.

The heat generated can be transferred to a final heat sink external tothe building in which the processors are located, for example to theatmospheric air surrounding the building. Current implementationstypically rely on air as the transfer medium at one or more stagesbetween the processors and the final heat sink.

However, it is difficult to use air as a transfer medium for such alarge quantity of heat, without imposing significant limitations on thebuilding infrastructure. This is because the rate at which heat can betransferred increases with: increasing temperature difference (ΔT)between the heat source (such as the server boards, in particular thecomputer processors) and final heat sink; and decreasing thermalresistance of the path or paths thermally connecting the heat source andfinal heat sink.

Some known technologies for dealing with this difficulty are designed tocontrol the environmental conditions of the location at which theprocessors are housed. Air handling techniques are currently often used,for example: vapour-compression refrigeration (“air conditioning”) ofthe air that reduces the local air temperature to increase the localtemperature difference; and air pressurisation (by the use of fans) toincrease the air flow rate and thereby reduce the thermal resistance.Further heat exchange stages may be used to transfer heat extracted fromthe local air to a final heat sink, such as atmospheric air.

However, these approaches can be inefficient, as the use of airconditioning can require substantial amounts of electrical power tooperate. These approaches can also make the location unpleasant forpeople, due to the local temperature and noise.

Furthermore, air flow rates and air temperatures may have to be limited,for example maintaining temperature above the “dew point” to preventwater vapour condensing out of air that may damage sensitive electroniccomponents. For these reasons, servers are currently commonlydistributed sparsely in order to reduce the heat density and improvelocal air flow, thereby reducing the thermal resistance.

Cooling the electronic components using a liquid that is brought intocontact with the electronic components can be used to increase serverdensity, reduce cooling costs or both.

An existing technique for cooling electronic components using a liquidis described in US-2007/109742 and GB-A-2432460. A computer processorboard is housed inside an airtight container. A coolant liquid,preferably oil, is pumped through the container. The processor board islocated at the bottom of the container and an evaporator coil ispositioned at the top of the container, such that convection currentsare produced in the coolant liquid. The coolant liquid is heated by theprocessor board and resultant vapour flows into a condenser. Thecontainer is positioned such that the circuit board inside lies in ahorizontal plane to allow convection of heat from the components.

Using a condenser to provide refrigeration increases the complexity andcost of the system, and introduces further limitations on the systemimplementation.

WO-2006/133429 and US-2007/034360 describe an alternative known approachfor cooling electronic components. The electronic component is sealedinside a container filled with a liquid and a thermally conductive plateis provided as part of the container in contact with the liquid. Thethermally conductive plate conducts heat from the liquid to the outsideof the container. Although this is designed for independent operation,the thermally conductive plate can be coupled to a further heatexchanger for additional cooling of the electronic component.

This alternative arrangement reduces the complexity of the system incomparison with approaches requiring pumped fluids inside the container.However, this does not significantly address the difficulty in reducingthe thermal resistance between the heat source and the final heat sink.Even if the temperature difference is increased, the total thermalresistance will still be significant.

SUMMARY OF THE INVENTION

Against this background and in a first aspect, the present inventionprovides a sealable module for containing one or more heat generatingelectronic components. The module comprises: a housing; a heat transferdevice having a conduction surface, the housing and the conductionsurface together defining a volume in which a first cooling liquid canbe located, the heat transfer device further defining a channel forreceiving a second cooling liquid, the conduction surface separating thevolume and the channel to allow conduction of heat between the volumeand the channel through the conduction surface; and an electroniccomponent located in the volume. At least a portion of the conductionsurface or housing is shaped in conformity with the shape of theelectronic component.

By conforming the shape of the housing, the conduction surface or bothto the shape of the electronic component, the efficiency of heattransfer between the first cooling liquid and second cooling liquid issignificantly increased. This makes it possible to maintain the firstcooling liquid in a liquid state up to a high level of heat output fromthe electronic component.

In the preferred embodiment, the sealable module further comprises atleast one electronic component which generates heat when in use, and afirst cooling liquid, located in the volume.

The second liquid coolant is caused to flow in the channel in directcontact with the conduction surface. The second liquid coolant ispreferably pumped. Transferring heat by conduction from a first coolingliquid in the volume to the second cooling liquid in the channel reducesthe thermal resistance significantly. This increases the efficiency ofheat transfer, making such a system scalable and applicable to systemswhich generate large quantities of heat, such as data processingcentres. Moreover, the reduced thermal resistance of this system gainedby using a conduction surface to transfer heat allows the coolant to bemaintained in a liquid state at all times, thereby avoiding the need forvapour-cycle refrigeration that increases the complexity and cost of thesystem.

Also, the electricity consumption for cooling is reduced by mitigatingor even eliminating the need for vapour-compression refrigeration. Thisalso allows the density of electronic components and electronic circuitboards, such as server boards, to be increased.

For a given density of servers and components, a cooling systemdesirably removes sufficient heat from each component to keep it withinits intended operating temperature range, but no more than that. Devicesthat generate less heat need less cooling than those that generatelarger amounts. Cooling below a level necessary for satisfactoryoperation will normally consume unnecessary additional energy and istherefore less than optimally efficient.

Beneficially, the channel has an area of contact with the conductionsurface defining a channel width, and wherein the minimum channel widthis significant in comparison with the dimensions of the conductionsurface.

Additionally or alternatively, the channel interfaces with theconduction surface along a path having at least one change in direction.Preferably, the path has a straight portion, and wherein the minimumchannel width is at least 10% of the length of the straight portion ofthe path. In other embodiments, the minimum channel width may be atleast: 10%; 20%; 30%; 40%; or 50% of the length of the straight portionof the path. Additionally or alternatively, the path comprises a mainpath and a branch path, the branch path being connected to the main pathat at least one point. More turbulent flow of liquid can improve heattransfer.

In a second aspect, the present invention provides a method of coolingan electronic component, comprising: providing a module comprising ahousing and a heat transfer device having a conduction surface, thehousing and the conduction surface together defining a volume; housingthe electronic component within the volume; filling the volume with afirst cooling liquid; and conducting heat between the first coolingliquid and a second cooling liquid through the conduction surface, thefirst cooling liquid and second cooling liquid being located on eitherside of the conduction surface. At least a portion of the conductionsurface or housing is shaped in conformity with the shape of theelectronic component.

Preferably, the step of conducting heat from the first cooling liquid toa second cooling liquid is configured such that the first cooling liquidand second cooling liquid remain in liquid state.

In a third aspect of the present invention, there may be providedsealable module kit, comprising: a housing; a heat transfer devicehaving a conduction surface, the heat transfer device being configuredto couple to the housing such that the conduction surface and housingdefine a volume in which a first cooling liquid can be located, the heattransfer device further defining a channel for receiving a secondcooling liquid such that when the heat transfer device is coupled to thehousing, the conduction surface separates the volume and the channel toallow conduction of heat between the volume and the channel through theconduction surface; and an electronic component for location in thevolume. At least a portion of the conduction surface or housing isshaped in conformity with the shape of the electronic component.

A number of additional features can be applied to the invention asspecified by any one of the first, second or third aspects specifiedabove. These will be described below.

Beneficially, the conduction surface has at least one projection intothe first volume for conducting heat between the volume and the channel.The use of at least one projection increases the surface area of theconduction surface and can allow closer conformity between theconduction surface and the shape of the electronic component. Theseimprove the efficiency of heat conduction.

Where the sealable module includes the electronic component, theconduction surface preferably has at least one projection into the firstvolume for conducting heat between the volume and the channel, the atleast one projection being arranged in conformity with the shape of theelectronic component. This further improves heat conduction efficiency,by: reducing the space between the component and the conduction surface;increasing total projection surface area to reduce thermal resistance inthe heat flow path; reducing the volume of cooling liquid required forefficient cooling; permitting the increased use of materials with poorerconductivity but reduced cost or weight or both (e.g. plastic). Inparticular, efficiency of cooling is improved if the cooling liquidcomes quickly into contact with the conduction surface.

Optionally, the conduction surface is made from a synthetic plasticmaterial, which is desirably thermally conductive. Additionally oralternatively, the housing may be made from a synthetic plasticmaterial. Preferably, this is thermally insulating. In embodiments, theheat transfer device may be made from a synthetic plastic material.

In some embodiments, the sealable module further comprises a componentheat sink coupled to the electronic component, having at least oneprojection arranged to cooperate with the at least one projection of theconduction surface.

Advantageously, the at least one projection of the conduction surfacecomprises a fin arrangement. Alternatively or additionally, the at leastone projection of the conduction surface comprises a pin arrangement. Inthe preferred embodiment, the at least one projection comprises apin-fin arrangement. The pin-fin projections may vary in height.Preferably, they are fin-shaped with a rectangular cross section. Morepreferably, the projections do not cover the whole conduction surface.

Preferably, a flow diverter is located in the volume. This may take theform of a baffle plate or other passive flow control mechanism. Such afeature has the purpose of deflecting hot rising plumes of liquid awayfrom components directly above that might otherwise over-heat.

Optionally, a plurality of electrical conductors are located in thevolume, the plurality of electrical conductors being arranged to detectthe level of the first cooling liquid. These electrical conductorspreferably take the form of a pair of rods at the top of the moduleextending down into the volume. These can act as a capacitor, whosevalue changes as the liquid level alters (by application of thedielectric effect). By attaching a suitable electronic circuit, theliquid level for the first cooling liquid can be deduced. This allowsthe operator to know when the level is below normal for the currentliquid temperature and indicates the likelihood of a leak. The samedevice could be used to determine liquid level during initial filling(or topping up) of the module.

Additionally or alternatively, a transparent window in the housing isused to observe the level directly. A further optional improvement wouldbe to build the sensor and associated circuit into a circuit board onwhich the electronic component is mounted or adjacent to the electroniccomponent.

In some embodiments where the conduction surface defines the channel,the shape of the channel is arranged in conformity with the shape of theelectronic component. This allows further improvements in efficiency ofheat transfer between the first cooling liquid and second coolingliquid.

In the preferred embodiment, the heat transfer device is formed in onepiece. A one piece assembly for the heat transfer device may not requiremaintenance and could be constructed from a cold plate part into whichchannels were pre-formed and a sealing plate welded or otherwise adheredonto the cold plate part. This eliminates screws and gaskets and reducesthe likelihood of liquid leakage.

In some embodiments, the heat transfer device further comprises a basepart coupled to the conduction surface and defining the channel forreceiving the second cooling liquid.

In one embodiment, the housing and conduction surface defines an innerchamber, and the heat transfer device further comprises an outerchamber, defining the channel.

The use of an outer chamber that defines the channel for receiving asecond cooling liquid and which is arranged to cooperate with the innerhousing to provide the conduction surface advantageously provides acompact module. Such an arrangement may additionally allow the width ofthe channel to be defined or adjusted to meet the heat transferrequirements. Optionally, the outer chamber is made from a syntheticplastic material.

Advantageously, the sealable module further comprises an insulationlayer covering at least part of the housing. Preferably, the insulationlayer is within the volume. Additionally or alternatively, the sealablemodule may comprise an insulation layer covering at least part of thehousing, exterior to the volume. The exterior insulation may compriseflexible foam. This has the further advantage of being able to supportthe connectors for liquid input, output or both, whilst allowing anelement of flexing of the pipes. This would make insertion into anassociated rack easier by allowing more tolerance in the sliding parts.

Preferably, more than one electronic component may be located in thevolume. In the preferred embodiment, the sealable module comprises aplurality of electronic components, at least one of which generates heatwhen in use, and further comprising a circuit board holding theplurality of electronic components.

By immersing the circuit board in a carefully selected liquid, it isisolated from damage by airborne pollutants or water that mightotherwise condense out of the atmosphere, or leak elsewhere. Pollutantspresent in air or dissolved in water can readily attack the fine wiringon circuit boards, for example. Also, other heat generating componentssuch as power supplies, DC-DC converters and disk drives can beencapsulated and cooled. Where the at least one electronic componentincludes a disk drive, the disk drive is preferably a solid statedevice. Devices with moving parts are undesirable for immersion in aliquid.

The first cooling liquid preferably occupies a portion of the volume ofthe sealable module, such that there is volume available for expansionof the liquid upon heating without significantly increasing the pressurein the volume.

Preferably, the sealable module further comprises a protective membranepositioned between the circuit board and the housing, the protectivemembrane being arranged to prevent liquid flow between the housing andthe circuit board. This increases the thermal resistance through thisundesirable path and reduces the volume of the coolant required to fillthe volume, whilst allowing for the presence of small components on therear of a circuit board. In the preferred embodiment, the protectivemembrane is deformable.

Advantageously, at least a part of the circuit board is integrallyformed with the housing. The electronic circuit board could beintegrated with part of the module housing, for example just using sidewalls. The interconnections could then pass directly through the circuitboard to appear on the outer face of the housing, eliminating the needfor cables to be sealed at the point of exit with the module.Optionally, the circuit board and walls are constructed as a single itemthus reducing further the sealing issue, for example using a fibreglassmoulding.

In the preferred embodiment, the sealable module further comprises: afilling inlet to the module, located in the housing and through which aliquid can be received into the volume; and a seal to the filling inlet.This allows quick filling or re-filling of the sealable module volumewith cooling liquid in field.

Preferably, the sealable module comprises a pressure relief valve,located in the housing and arranged to allow liquid flow out from thevolume when the pressure within the volume exceeds a predefined limit.

Optionally, the channel has an area of contact with the conductionsurface defining a channel width, and wherein the minimum channel widthis significant in comparison with the dimensions of the conductionsurface.

Additionally or alternatively, the channel interfaces with the at leasta portion of the conduction surface along a path having at least onechange in direction. Preferably, the path has a straight portion, andwherein the minimum channel width is at least 10% of the length of thestraight portion of the path. In other embodiments, the minimum channelwidth may be at least: 10%; 20%; 30%; 40%; or 50% of the length of thestraight portion of the path. Additionally or alternatively, the pathcomprises a main path and a branch path, the branch path being connectedto the main path at at least one point.

The present invention can also be found in a cooled electronic system,comprising: the sealable module as described herein; an electroniccomponent located in the volume; a first cooling liquid located in thevolume; a heat sink; a pumping arrangement, arranged to allow a secondcooling liquid to flow through at least a portion of the channel of thesealable module to the heat sink at a predetermined flow rate; atemperature sensor, arranged to determine a temperature of theelectronic component; and a controller arranged to control at least oneof: the pumping arrangement; and the portion of the channel throughwhich the second cooling liquid flows, such that the temperature of theelectronic component is controlled so as not to exceed a predeterminedmaximum operating temperature.

Beneficially, the conduction surface has at least one projection intothe first volume for conducting heat between the volume and the channel.Where the sealable module includes the electronic component, theconduction surface preferably has at least one projection into the firstvolume for conducting heat between the volume and the channel, the atleast one projection being arranged in conformity with the shape of theelectronic component. In some embodiments, the sealable module furthercomprises a component heat sink coupled to the electronic component,having at least one projection arranged to cooperate with the at leastone projection of the conduction surface. Advantageously, the at leastone projection of the conduction surface comprises a fin arrangement.Alternatively or additionally, the at least one projection of theconduction surface comprises a pin arrangement. In the preferredembodiment, the at least one projection comprises a pin-fin arrangement.

A fourth aspect of the invention may be found in a method of cooling anelectronic device, comprising: providing a module comprising a housingand a first heat transfer device having a conduction surface, thehousing and the conduction surface together defining a volume, thevolume being filled with a first cooling liquid and having theelectronic device located therein; operating the electronic devicewithin the volume; transferring heat generated by the electronic devicefrom the first cooling liquid to a second cooling liquid through atleast a portion of the conduction surface; transferring heat from thesecond cooling liquid to a heat sink using a second heat transferdevice; and setting one or both of: the flow rate of the second coolingliquid from the conduction surface to the heat sink; and the portion ofthe conduction surface through which heat is transferred to the secondcooling liquid, such that the temperature of the electronic device iscontrolled so as not to exceed a predetermined maximum operatingtemperature.

By setting the flow rate, area of heat transfer or both, the thermalresistance can advantageously be increased or reduced as needed toprovide the desired temperature difference. This allows the electroniccomponent to be maintained at a temperature no greater than its maximumoperating temperature, even if the temperature difference decreases, forexample, if the final heat sink temperature increases (such as when anatmospheric final heat sink is used). Optionally, the conduction surfaceis made from a synthetic plastic material.

Optionally, the method further comprises: determining a temperature ofthe electronic component. The step of setting is carried out on thebasis of the determined temperature. This is a form of dynamicadjustment based on measured temperature.

Additionally or alternatively, the step of setting comprises at leastone of: the flow rate of the second cooling liquid from the conductionsurface to the heat sink; and the portion of the conduction surfacethrough which heat is transferred to the second cooling liquid being setto a predetermined level on the basis of a predicted predeterminedmaximum operating temperature for the electronic device. In suchembodiments, the flow rate, portion of the conduction surface or bothare pre-set based on a predicted heat output or heat output range fromthe electronic device.

In a fifth aspect, there is provided a cooled electronic system,comprising: a sealed container comprising: a housing; an electronicdevice; and a first cooling liquid; a first heat transfer devicedefining a first channel for receiving a second cooling liquid, thefirst heat transfer device being configured to transfer heat between thefirst cooling liquid and the first channel through at least a portion ofa conduction surface; and a piping arrangement, configured to transferthe second cooling liquid to and from the first heat transfer device.The system is configured to set one or both of: the flow rate of thesecond cooling liquid through the first channel; and the portion of theconduction surface through which heat is transferred to the secondcooling liquid, such that the temperature of the electronic device iscontrolled so as not to exceed a predetermined maximum operatingtemperature. Advantageously, the second cooling liquid flows from theconduction surface to a heat sink.

A sixth aspect of the invention may be provided by a method of coolingan electronic device, comprising: operating the electronic device withina container, the container also comprising a first cooling liquid, suchthat heat generated by the electronic device is transferred to the firstcooling liquid, the container being sealed to prevent leakage of thefirst cooling liquid; transferring heat between the first cooling liquidand a second cooling liquid in a first heat transfer device; piping thesecond cooling liquid from the first heat transfer device to a secondheat transfer device; transferring heat between the second coolingliquid and a third cooling liquid in the second heat transfer device;and piping the third cooling liquid to a heat sink.

Thus, three stages of liquid cooling are provided, which allows the flowrate and pressure of the second cooling liquid and third cooling liquidto be independently controlled. The pressure of second cooling liquidcan therefore be reduced to further mitigate the risk of leakage of thisliquid. Since these liquids are in close proximity to the electroniccomponents, leakage is undesirable. Also, the flow rates canadvantageously be controlled based upon the level of heat generated toimprove the efficiency of heat transfer at each stage.

Preferably, the step of transferring heat between the first coolingliquid and the second cooling liquid is carried out by conduction.

In the preferred embodiment, the method further comprises: controllingthe flow rate of the second cooling liquid, such that the temperature ofthe electronic device does not exceed a predetermined maximum operatingtemperature. Additionally or alternatively, the method may alsocomprise: controlling the flow rate of the third cooling liquid, suchthat the temperature of the electronic device does not exceed apredetermined maximum operating temperature. This allows the flow rateof second cooling liquid to be matched to the level or rate of heatgeneration.

Where the first heat transfer device comprises a conduction surface, themethod optionally further comprises setting the portion of theconduction surface through which heat is transferred to the secondcooling liquid, such that the temperature of the electronic device iscontrolled so as not to exceed a predetermined maximum operatingtemperature. This can be achieved, for example, using multiple channelsin the conduction surface for carrying the second cooling liquid andappropriate control valves or baffle plates to determine the channel orchannels along which the second cooling liquid should flow, or tobalance the flow rate of cooling liquid appropriately between differentchannels in order to maintain the temperature of the electronic devicebelow a threshold. The channels thereby provide similar or differentliquid flow rates over different areas and thus different heat transferrates from different parts of the conduction surface.

In some embodiments, the method may further comprise controlling atleast one of: the flow rate of the second cooling liquid; and the flowrate of the third cooling liquid, such that the temperature of theelectronic device does not exceed a predetermined maximum operatingtemperature and such that, during a first time period, the heat transferrate between the second cooling liquid and the third cooling liquid orbetween the third cooling liquid and the heat sink does not go above apredetermined maximum rate, and such that during a second, later timeperiod, the heat transfer rate between the second cooling liquid and thethird cooling liquid or between the third cooling liquid and the heatsink may go above the predetermined maximum rate.

Optionally, the step of controlling is carried out such that thetemperature of the electronic device does not exceed a predeterminedmaximum operating temperature and such that, during a first time period,the temperature of at least one of: the second cooling liquid; and thethird cooling liquid does not go below a predetermined minimum averagetemperature, and such that during a second, later time period, thetemperature of the second cooling liquid and the third cooling liquidmay go below the predetermined minimum average temperature.

In a further aspect of the present invention, there is provided a methodof cooling an electronic device, comprising: operating the electronicdevice within a container, the container also comprising a first coolingliquid, such that heat generated by the electronic device is transferredto the first cooling liquid, the container being sealed to preventleakage of the first cooling liquid; transferring heat between the firstcooling liquid and a second cooling liquid in a first heat transferdevice; transferring heat between the second cooling liquid and a heatsink; and controlling the heat transfer rate between the second coolingliquid and the heat sink, such that the temperature of the electronicdevice does not exceed a predetermined maximum operating temperature andsuch that, during a first time period, the heat transfer rate does notgo above a predetermined maximum rate, and such that during a second,later time period, the heat transfer rate may go above the predeterminedmaximum rate.

An advantageous feature of the system used in the method is the highthermal capacity of the cooling arrangement. This has a number ofbenefits and opportunities. Failure of a part of the system will notlead to immediate component damage. The temperature will rise but notquickly, giving maintenance staff more time to isolate the faulty partand minimise further failures. Similarly, the system is able to copewith environments with high diurnal ambient temperature variations. Heatbuilt up during the day can be tolerated by the system without exceedingmaximum component operating temperatures. The heat can be safelydissipated at night to the cold. The system flow management algorithmmay be arranged to take account of such high diurnal ambient variations.

Advantageously, a method of cooling an electronic system is provided,comprising: carrying out the method steps of cooling an electronicdevice in accordance with this sixth aspect; operating a secondelectronic device within a second container, the second container alsocomprising a fourth cooling liquid, such that heat generated by theelectronic device is transferred to the fourth cooling liquid, thesecond container being sealed to prevent leakage of the fourth coolingliquid; and transferring heat between the fourth cooling liquid and afifth cooling liquid in a third heat transfer device. Optionally, themethod further comprises controlling the flow rate of the fifth coolingliquid.

A unit with two containers may be heavy and difficult to install in arack, as they could exceed health and safety limits for a one-personlift. In one embodiment, first and second containers are used and thesecontainers are provided back-to-back. In other words, the connectors ofthe first container are positioned adjacent to the connectors of thesecond container. Back-to-back containers with centralised cabling andliquid pipes in a rack would allow units with one module and singleperson lift.

Preferably, the second cooling liquid and the fifth cooling liquid arecombined. This allows efficient cooling of multiple electronic devicesusing separate first cooling stages, but a common second stage ofcooling. More preferably, the method further comprises piping the secondcooling liquid from the first heat transfer device and the fifth coolingliquid from the third heat transfer device to a plenum chamber. Mostpreferably, the second cooling liquid and the fifth cooling liquid arecombined before arrival at the plenum chamber. Optionally, the methodalso comprises: piping the second cooling liquid from a plenum chamberto the first container and piping the fifth cooling liquid from theplenum chamber to the second container.

Optionally, the method further comprises controlling the flow rate ofthe combined second cooling liquid and fifth cooling liquid, such thatthe temperature of the first electronic device does not exceed a firstpredetermined maximum operating temperature and such that thetemperature of the second electronic device does not exceed a secondpredetermined maximum operating temperature.

In this embodiment, individual flow control, per module, is notnecessary. The overall flow rate of the combined liquid can becontrolled with satisfactory results, when combined with pre-set flowbalancing of liquid to each cooling unit, for example, by means ofbaffles in the supply side plenum chamber.

In an alternative embodiment, the method further comprises: piping thefifth cooling liquid from the third heat transfer device to a fourthheat transfer device; and transferring heat between the fifth coolingliquid and the third cooling liquid in the fourth heat transfer device.

In an seventh aspect, the present invention may be found in a cooledelectronic system, comprising: a sealed container comprising: a housing;an electronic device; and a first cooling liquid; a first heat transferdevice defining a first channel for receiving a second cooling liquid,the first heat transfer device being configured to transfer heat betweenthe first cooling liquid and the first channel; and a second heattransfer device comprising a second channel for receiving the secondcooling liquid from the first channel, and a third channel for receivinga third cooling liquid for coupling to a heat sink, the second heattransfer device being configured to transfer heat between the secondchannel and the third channel.

Preferably, the first heat transfer device comprises a conductionsurface, the housing and the conduction surface together defining avolume in which the electronic component and the first cooling liquidare located. More preferably, the conduction surface separates thevolume and the first channel to allow conduction of heat between thevolume and the channel through the conduction surface.

Beneficially, at least a portion of the conduction surface or housing isshaped in conformity with the shape of the electronic device.

Advantageously, the conduction surface has at least one projection forreceiving heat from the first cooling liquid. In the preferredembodiment, the at least one projection is arranged in conformity withthe shape of the electronic device. Optionally, the cooled electronicsystem further comprises a component heat sink coupled to the electronicdevice and comprising at least one projection arranged to cooperate withthe at least one projection of the conduction surface.

Beneficially, the at least one projection of the conduction surfacecomprises a fin arrangement. Alternatively or additionally, the at leastone projection of the conduction surface comprises a pin arrangement. Inthe preferred embodiment, the at least one projection comprises apin-fin arrangement.

In one embodiment, the heat transfer device further comprises a basepart coupled to the conduction surface and defining the channel forreceiving the second cooling liquid.

Advantageously, the conduction surface is made from a synthetic plasticmaterial. Additionally or alternatively, the housing may be made from asynthetic plastic material. In embodiments, the base part of the heattransfer device may be made from a synthetic plastic material.

Optionally, the module further comprises: a filling inlet to thecontainer, through which the first cooling liquid can be received; and aseal to the filling inlet. Additionally or alternatively, the modulefurther comprises a pressure relief valve, arranged to allow outflow ofthe first cooling liquid from the container when the pressure within thecontainer exceeds a predefined limit.

Where the electronic device has an elongate axis, the conduction surfacepreferably has an elongate axis arranged in conformity with the elongateaxis of the electronic device to allow conduction of heat between thevolume and the channel through the conduction surface.

Optionally, the cooled electronic system further comprises a flowcontrol device, arranged to control the flow rate of the second coolingliquid, such that the temperature of the electronic device does notexceed a predetermined maximum operating temperature.

Additionally or alternatively, the cooled electronic system may furthercomprise a flow control device, arranged to control the flow rate of thethird cooling liquid, such that the temperature of the electronic devicedoes not exceed a predetermined maximum operating temperature.

In some embodiments, the sealed container is a first sealed container,and the cooled electronic system further comprises: a second sealedcontainer comprising: a second housing; a second electronic device; afourth cooling liquid for receiving heat from the second electronicdevice; and a third heat transfer device comprising a fourth channel forreceiving a fifth cooling liquid, the third heat transfer device beingconfigured to transfer heat from the fourth cooling liquid to the fourthchannel.

Preferably, the first channel and the fourth channel are coupled tocombine the second cooling liquid and the fifth cooling liquid.Optionally, the cooled electronic system further comprises a plenumchamber, arranged to collect the combined second cooling liquid andfifth cooling liquid.

Advantageously, the cooled electronic system further comprises a flowcontrol device, arranged to control the flow rate of the combined secondcooling liquid and fifth cooling liquid, such that the temperatures ofthe first electronic device and the second electronic device do notexceed first and second predetermined maximum operating temperaturesrespectively.

Preferably, the flow control device comprises a flow divertingarrangement, the flow diverting arrangement being configured to set theflow rate of the second cooling liquid such that the temperature of thefirst electronic device does not exceed a first predetermined maximumoperating temperature, and to set the flow rate of the fifth coolingliquid such that the temperature of the second electronic device doesnot exceed a second predetermined maximum operating temperature.

Alternatively, the cooled electronic system further comprises a fourthheat transfer device comprising a fifth channel for receiving the fifthcooling liquid from the fourth channel, and a sixth channel forreceiving a sixth cooling liquid for coupling to a heat sink, the secondheat transfer device being configured to transfer heat between the fifthchannel and the sixth channel.

In an eighth aspect, the present invention may be found in a method offilling the interior a container for an electronic device with a coolingliquid, the method comprising: adapting the container to receive thecooling liquid by at least one of: heating the container to a fillingtemperature; and reducing the pressure in the interior of the container;filling the container with the cooling liquid; and sealing the containerto prevent leakage of the cooling liquid.

By adapting the container and liquid to a filling temperature orpressure and filling the container with the liquid at this temperatureor pressure, the volume of the interior space of the container that isfilled with liquid under operating conditions is increased, withoutsignificantly increasing the pressure within the container. Excessivepressure may result in damage to the container or the electronic device.

Optionally, the method further comprises: heating the cooling liquid tothe filling temperature; and cooling the sealed container and coolingliquid to an operating temperature.

In some embodiments, the step of filling the container is carried outbefore the step of adapting the container. Optionally, the step ofadapting the container comprises operating the electronic device.

In a ninth aspect, there is provided a method of filling the interior acontainer for an electronic device with a cooling liquid, the methodcomprising: heating the cooling liquid to a filling temperature; fillingthe container with the heating cooling liquid; sealing the container toprevent leakage of the cooling liquid; and cooling the sealed containerand cooling liquid to an operating temperature. This is an alternativeto the eight aspect and the eighth and ninth aspects can also optionallybe combined.

In either or both of the eighth and ninth aspects, there are a number ofpreferable or optional features. Advantageously, the filling temperatureis selected such that gases dissolved in the cooling liquid are removedfrom the cooling liquid. Hence, air, moisture and other dissolved gasesare removed from the interior of the container. The need for a desiccantin the container is reduced or avoided.

Preferably, the filling temperature is selected on the basis of themaximum operating temperature of the electronic device. Beneficially,the filling temperature is selected to be equal to or greater than themaximum operating temperature of the electronic device.

In the preferred embodiment, the step of filling the container iscarried out such that all air in the container is displaced.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be put into practice in various ways, one of whichwill now be described by way of example only and with reference to theaccompanying drawings in which:

FIG. 1 shows a simplified front view of an equipment rack containingmultiple cooling units, each cooling unit comprising two sealablemodules according to the invention;

FIG. 2 is a simplified cross-sectional side view of the equipment rackshown in FIG. 1;

FIG. 3 illustrates a cooling unit, as shown in FIG. 1, fitted with acover;

FIG. 4 depicts a cooling unit with its cover removed, showing twosealable modules according to the invention;

FIG. 5 is a cross-sectional exploded view of a sealable modulecomprising a heat generating electronic component according to anembodiment of the invention;

FIG. 6 is a cross-sectional view of the upper part of the sealablemodule of FIG. 5;

FIG. 7 shows the sealable module face of an embodiment of a cold plate,for use with the sealable module of FIG. 5;

FIG. 7A shows an embodiment of the opposite face of a cold plate fromthat shown in FIG. 7, showing liquid flow channels for a second coolingliquid, for use with the sealable module of FIG. 5;

FIG. 7B shows an alternative embodiment of the face of the cold plate 60shown in FIG. 7A;

FIG. 8 is a schematic view of a three-stage cooling system comprising asingle cooling unit according to the invention;

FIG. 9 is a block diagram showing a three-stage cooling system withmultiple cooling units according to the invention;

FIG. 10 shows a monitoring and control system for use with thethree-stage cooling system of FIG. 9;

FIG. 11A shows a first side view of a second embodiment of a sealablemodule according to the present invention;

FIG. 11B shows a second side view of the embodiment shown in FIG. 11A;and

FIG. 11C shows a more detailed view of the embodiment shown in FIG. 11Aand FIG. 11B.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring first to FIG. 5, there is shown a cross-sectional explodedview of a sealable module 41 comprising a heat generating electroniccomponent 69 according to an embodiment of the invention. The sealablemodule comprises: a housing 81; a finned conduction surface 71 formingpart of a cold plate 60; a container volume, defined after assembly ofthe components by the housing 81 and conduction surface 71 and filledwith a first cooling liquid (not shown); liquid flow channels 61adjacent the conduction surface 71; small electronic component 68; largeelectronic component 69; and memory module 76.

The sealable module further comprises: an electronic circuit board 75;mounting pillars 63 for the electronic circuit board 75; a componentheat sink 70 attached to the large electronic component 69; screws 80 toattach the mounting pillars 63 to the conduction surface 71; a coverplate 78 for the side of the cold plate opposite to the fins on theconduction surface; insulation 73 for the housing 81; first sealinggasket 62; second sealing gasket 64; screws 79 to hold the components ofthe cold plate assembly together; and pin-fin projections 65 on theconduction surface 71. The insulation 73 can also serve as a protectivemembrane between the housing 81 and the circuit board 75.

The cold plate 60 is fabricated with two faces, each with a separatefunction. Conduction surface 71 is a pin-finned plate, forming one faceof the cold plate. A housing 81 is attached to the pin-finned plate 71,in such a way as to provide an internal space for an electronic circuitboard 75, the pins of the cold plate and a first cooling liquid (notshown). A gasket 62 ensures that the assembled capsule is substantiallysealed against liquid loss or ingress of air. The pin-finned plate iseffectively the lid of the assembled capsule.

The electronic circuit board 75 carrying components to be cooled isattached to the cold plate 60 by mounting pillars 63, so as to suspendthe board from the cold plate 60, allowing accurate alignment of thefins of the cold plate with components on the board, prior to attachingthe housing 81.

Alternatively, the board may be attached to housing 81 by mountingbosses extending from the housing 81 or equivalent means.

The fins 65 of the pin-finned conduction surface 71 normally face thecomponent side of the circuit board 75. In some cases, components ofsignificant size may be present on both sides of the board. The housingmay then be contoured around the components on the side of the boardopposite the pin-finned conduction surface 71, in order to improve flowof the cooling liquid and reduce the amount of cooling liquid needed.

In the embodiment shown in FIG. 5, the cold plate is fabricated in asingle part, with two separately formed faces. Alternatively, the platemay be manufactured in two parts: a pin-finned plate whose opposite faceis flat; and a plate with channels 61 for liquid flow, again with a flatopposite face; the two flat faces being joined on assembly. The coldplate assembly 60 has a surface opposite to the pin-finned conductionsurface into which channels whose cross section is shown at 61 aremanufactured.

The component side of the electronic circuit board 75 faces the fins 65on the conduction surface 71. A small gap between the ends of the finsand the components is provided. The fins have an elongated cross-sectionand the height of the fins varies, so as to maintain a small gap betweenthe variously sized components on the electronics circuit board and thetops of the fins. The faces of the electronic components 68 and 69 andthe edge of the memory module 76 project by different amounts from thesurface of the board. Small component 68 has a relatively low profileand large component 69 has a much deeper profile and the correspondingfins 65 have accordingly different heights. The height of the pin-finsand the gap between components on the circuit board 75 and the top ofthe pin-fins are arranged to be as small as possible, consistent withthe requirement for efficient cooling. This arrangement reduces thetotal quantity of cooling liquid needed in the capsule and improvespacking density of cooling units.

When the system is in operation, heat generated by the components 68, 69and memory module 76 on the circuit board is transferred to the coolingliquid (not shown), initially by local conduction and then, as theheated liquid expands and becomes buoyant, by convection. The convectingliquid quickly comes into contact with the fins 65 and other surfaces ofthe conduction surface 71.

Heat from the fins 65 of the conduction surface 71 is conducted to thecirculating second liquid that flows via channels 61, so as to cool theconduction surface 71 and thus cooling liquid.

Components on circuit board 75 that generate the largest amount of heatare typically microprocessors. In this case, cooling efficiency for suchcomponents may be improved by additionally fitting a finned componentheat sink 70, in direct physical and thermal contact with the component,whose fins may interleave with the array of fins on the cold plate. Thefins of the component heat sink may be at least partially in physicalcontact with the pin-fins of the cold plate. Gaps remain through whichthe first cooling liquid can flow.

An additional insulating layer 73 is provided, preferably on the insideof the housing 81 of the sealable module 41. Additional insulation mayalso be added to the exterior of the cold plate cover 78 and to theedges of the cold plate 60. The insulation reduces local heat loss intothe atmosphere, which can be significant in large installations withmany electronic circuit boards, causing room temperature to rise toundesirable levels.

Electronic circuit board 75 may carry major components only on one sideor the other side may carry only small components that generate lowamounts of heat in operation. The operation of the sealable module 41may then be improved by excluding liquid flow adjacent to thenon-component side of the circuit board 75. The insulation 73 may thenact as a flexible protective membrane between the circuit board 75 andthe housing 81, that can accommodate to the shape of the smallcomponents that may be mounted on this side of the board. Alternatively,a separate protective membrane (not shown) could be provided between thehousing 81 and the electronic circuit board 75. Convective flow of thecooling liquid is then concentrated in the space between the maincomponent side of the circuit board 75 and the conduction surface 71.

Application of the invention is not limited to computing systems.However, since computing systems generate significant heat, they canbenefit from improved cooling. In such systems, one or moremicroprocessors and several other digital and analogue devices such asmemory chips (RAM, ROM, PROM, EEPROM and similar devices), specialisedintegrated circuits (ASICs) and a range of associated active and passivecomponents are typically mounted on a circuit board, whose function isto act as a major part of a computing system. Although electroniccomponents can be mounted on both sides of the circuit board, it is moreusual to mount at least the bulky components on one side only. Otherdevices are connected to the circuit board by cables, optical means orwireless transmission, the whole forming a computer, computer system orserver.

Heat is generated by the various components but, typically, themicroprocessor is the highest heat-generating component. An optimallydesigned cooling system removes sufficient heat from each component tokeep it within its designed operating temperature range but no more thanthat. Devices that generate less heat need less cooling than those thatgenerate larger amounts. Cooling below a level necessary forsatisfactory operation will normally consume unnecessary additionalenergy and is therefore less than optimally efficient.

Moreover, packing density of components on computer boards is determinedpartly by the traditional size of computer housings and the assumptionthat air-cooling may be employed. In large systems, especially servercentres, increasing the packing density of components to reduce overallspace occupied is desirable. At the same time, heat generated will beconcentrated in a smaller space and needs more effective means ofremoval. Improving heat removal may enable component packing density tobe increased and, more particularly, allow processing power per unitvolume to increase.

Referring now to FIG. 6, there is shown a cross-sectional view of theupper part of the sealable module 41 of FIG. 5. Where the same featuresare shown, identical reference numerals are used. The depth of themodule is exaggerated to clarify details of some features that wouldotherwise be difficult to illustrate. FIG. 6 additionally shows: firstcooling liquid 66; a filling inlet 44; seal 43; a pressure relief device45; fastener 82 for receiving assembly screw 79; sealing gasket 62;baffle plate 74; and capacitive rods 72. The filling inlet 44 isintended for receiving the first cooling liquid 66 and has a seal 43 toprevent liquid loss once the sealable module 41 is filled. A pressurerelief device 45 allows escape of liquid under extreme conditions,outside a normal range of: temperature; pressure; or both.

Normally, larger components that generate the highest amount of heat arelocated towards the lower part of the module 41. In some circumstances,the heated liquid 66 may rise in a narrow convection plume that couldoverheat components located higher in the module. Baffle plate 74 maythen be fitted to deflect the hot plume of liquid away from thecomponents in the upper part of the module and aid mixing with coolerliquid for re-circulation within the module. Similarly, where two ormore processors that generate large amounts of heat are fitted tocircuit board 75, it is possible that one processor is above the otherand receives heated liquid from the lower mounted processor. A baffleplate 74 or a similar or equivalent means of passively deflecting hotliquid may then be fitted in the lower part of the module.

Typically, cooling liquid 66 is a volatile substance. Small leaks fromthe module may be difficult to detect, since the liquid may evaporatebefore being observed. Capacitive rods 72 may then be fitted in theupper part of the module 41, normally immersed in liquid 66 andconnected to an external detector (not shown) that measures thecapacitance. In the event that the liquid leaks from the module, thelevel of liquid 66 will drop and the capacitance will alter. If thecapacitance alters appreciably, an alarm can thus be generated,indicating excessive loss of liquid from the module. The capacitive rods72, the connections thereto and a detection circuit may alternatively bebuilt in to a customised electronic circuit board, thus simplifyingassembly of the complete capsule and removing the possibility of leakageof liquid from the entry point of the capacitive rods 72 into thehousing 81.

An alternative means of monitoring the liquid level is a smalltransparent window (not shown) that may also be fitted to the upper partof housing 81. This window allows direct observation of the level ofliquid 66 within the module.

Referring now to FIG. 7, there is shown one face of an embodiment of acold plate 60, for use with the sealable module 41 of FIG. 5. This faceprovides a pin-finned plate that attaches to housing 81 as shown in FIG.5 to form a sealable first stage cooling module. FIG. 7A shows theopposite face of the embodiment of the cold plate.

The face of cold place 60 shown in FIG. 7 comprises: conduction surface71; first pin-fin 96; second pin-fin 97; a channel 87 for a sealinggasket; and holes 88 for assembly screws to attach the housing 81 ofFIG. 5. The pin-fins 96 and 97 form projections from the conductionsurface 71.

An inlet 84 and outlet 83 for the second cooling liquid are visible inFIG. 7 but connect to the other side of the cold plate. Mounting lugs 90for the complete module also support the liquid inlet and outlet pipes83, 84. The pin-fins 96 are of greater height than pin-fins 97. Theillustrated pin-fins are examples and the actual layout and size ofpin-fins may vary according to the shape and heat-generatingcharacteristics of the components to be cooled.

Turning now to FIG. 7A, there is shown an embodiment of the oppositeface of the cold plate 60 to that illustrated in FIG. 7, for use withthe sealable module 41 of FIG. 5. Flow directing fingers 85, 89 createchannels 91 in the cold plate 60 that form a continuous winding patternwithin the boundary of the cold plate 60 and join via holes 92 to tubesthat emerge as inlet connector 84 and outlet connector 83 for the secondcooling liquid.

The flat part of this side of the cold plate 60 is the opposite side ofconduction surfaces 71 shown in FIG. 7. Cover 78 of FIG. 5 is attachedto the cold plate by screws that align with holes 88 and is sealed by agasket that fits in channel 87, so as to enclose the channels 91, thuscreating a winding channel arrangement within the assembly. Since theassembled arrangement of channels requires no maintenance, an improvedassembly may be constructed by welding the cover 78 directly to the coldplate 60 base part. Adhesive or other techniques for fixing the coverpermanently can alternatively be used. Gasket 64 and assembly screws arethen not required and the potential for leakage of the second coolingliquid is reduced.

Alternatively, the single winding channel arrangement may be branched toform two or more channels, with common input and output connections forthe second cooling liquid. The two or more channels may be of similar ordifferent dimensions, and may be winding or straight, so as to provide adifferent flow rate of second cooling liquid over different parts of thecold plate.

Turning to FIG. 7B, there is shown an alternative embodiment of the faceof the cold plate 60 shown in FIG. 7A. This illustrates one possiblearrangement with several channels, aligned generally in a verticalorientation. The channels are bounded by flow directing fingers 93. Theflow of liquid entering via inlet 84 is divided amongst the channels;the flow rate in each channel being dependent on the width of thechannel, the shape of the entrance to the channel and the location ofthe liquid entry hole 92.

Thus, it is possible to arrange the assembly so as to provide similar ordifferent liquid flow rates over different areas and thus different heattransfer rates from different parts of the plate. Electronic componentsadjacent to the conduction surface on the other side of plate 60 fromthe channels may generate different amounts of heat. With higher levelsof heat production, this may advantageously be made to correspond withthe areas with higher rates of heat transfer.

A degree of adjustment may, optionally, be included in the assembly. Oneor more adjustable baffle plates 94 attached by locking screws 95 may bepositioned so as to direct the flow of liquid more towards or away fromone of the channels. The baffle plate may be adjusted by slackeningscrew 95, rotating the baffle plate to a new position and thenre-tightening the screw. In this example, the adjustment is made beforethe cover is attached, although it would be readily possible to addmeans of adjusting the baffle plate from the exterior of the assembledunit.

Mounting lugs 90 for the complete assembly also support the inletconnector 84 and outlet connector 83.

The material used for the cold plate 60 and conduction surface 71 ischosen to be a good conductor of heat, typically a metal. For ease offabrication and lower cost in quantity production, a plastic materialcould be employed with lower but still adequate heat conductionproperties. The channels 91 formed within the cold plate 60 are used tocarry a second cooling liquid that circulates through the cold plate andthen outside to carry heat away to further cooling stages of the system.

The sealable modules 41 provide a first stage of cooling and form partof cooling units, each cooling unit carrying one or more modules. Atleast one and typically many first-stage cooling units are deployed in asystem. The cooling units may be fitted into any convenient housing but,where large numbers are used in a system, conventional equipment rackswould normally be used.

In FIG. 4, there is shown a cooling unit with its cover removed, showingtwo sealable modules. Where the same features are shown in FIG. 4 as inFIGS. 6 and 7, identical reference numerals are used. In addition isshown: frame 31; locking tabs 32; data transfer cable 46; power cable47; first seal for cable entry 50; second seal for cable entry 51; andtest and monitoring panel 52.

Essentially, FIG. 4 shows the sealable part of each cooling module 41,the remaining part being on the opposite side of the module, separatedby the internal cold plate and conduction surface of FIG. 5. The coolingunit comprises a frame 31, which supports cooling modules 41 and variousliquid and electrical interconnections. The front panel of the frame 31carries a test and monitoring panel 52 and locking tabs 32, which canrotate about a hinge so as to lock the unit in place in an equipmentrack.

Two sealed modules 41 are shown. The housing 81 for each sealable module41 is made of plastic or equivalent material, chosen to be an electricalinsulator, and to have heat insulating properties, as well as notreacting with the cooling liquid used in the module. Housing 81 is helddown by fasteners 56. Cables 46, 47, carrying electrical power andsupporting bi-directional data transmission enter the capsule via entrypoints 50 and 51, sealed to prevent the escape of liquid or the ingressof air. Cables 46, 47 terminate in respective connectors (not shown) atthe rear of the cooling unit.

The cold plate side of each module (not shown in FIG. 4) is cooled by acirculating second liquid. Each of the two sealable modules 41 isconnected via an inlet pipe 53 for the second cooling liquid, to aliquid flow splitter 55. The liquid flow splitter 55 has two outputs anda common input, connected by a further pipe 58. This splits the flow ofsecond cooling liquid between modules 41 and the common input isconnected by a further pipe 58 to liquid input connector 12 on the rearpanel of the cooling unit. Similarly, a liquid outlet pipe 54 from eachof the two sealable modules carries liquid to a flow-combining unit 57,the common output of which is connected by a further pipe 59 to liquidoutput connector 11 on the rear panel of the cooling unit.

The assembled sealable module 41 is partly or wholly filled with a firstcooling liquid 66 via the filling inlet 44 and then sealed with sealingdevice 43. The filling procedure may take place during factory assemblyor during field installation of cooling modules.

During filling, the sealable module 41 is partly filled with liquid, theremaining space being occupied by a mixture of its vapour and someresidual air. One method of achieving this is by heating the liquid andthe module to a filling temperature (T_(fill)), selected to be wellabove ambient temperature and approximately the same as the maximumoperating temperature of the system (T_(max)). The maximum storagetemperature of the electronic components is typically much higher thanmaximum operating temperature, so that T_(fill) can either be below,equal to or above T_(max), the highest envisaged operating temperatureof the system.

Liquid is then added to displace most of the air within the sealablemodule 41, such that the level of liquid is sufficient substantially toimmerse all the components to be cooled. The sealable module 41 is thensealed with sealing device 43 to prevent liquid escape and ingress offurther air. The sealable module 41 is then allowed to cool to roomtemperature. The liquid contracts and leaves a space, occupied by liquidvapour and air mixture. The filling procedure may take place in two ormore steps, allowing time for liquid that has been added to the sealablemodule 41 in one step to cool partly before adding more.

At ambient temperature, the vapour and air in the filled and sealedmodule is thus below atmospheric pressure. This can rise duringoperation so as be equal to or moderately higher than externalatmospheric pressure. A module filled at ambient temperature and thenimmediately sealed would, during operation and heating to T_(max), besubjected to much higher and potentially damaging internal pressure thanone filled by the method described.

The method may, if desired, be extended to exclude all air from theliquid by filling the module completely at T_(fill) and choosingT_(fill) to be higher than T_(max), so that, on cooling, the remainingspace above the liquid is filled only with vapour from the liquid at alow pressure below atmospheric. Heating the liquid has the additionalbenefit of driving out some or most of the dissolved gaseouscontaminants that may be present in the untreated liquid.

A further alternative method of filling is to add liquid via fillinginlet 44 to the module 41 when both are at ambient temperature, so as tofill to a pre-determined level, sufficient to immerse substantially theelectronic components to be cooled. Before sealing with seal 43, themodule is then connected to its power supplies and the electroniccomponents set into operation in such a way as to elevate the liquidtemperature to or close to T_(max). The module is then sealed,disconnected from its power supplies and left to cool.

Yet another method of filling is under vacuum, such that liquid can beadded to the module at ambient temperature, whilst all or most air isexcluded. One way of achieving this is to fit a valve and a means ofconnecting a tube for air to be pumped out and liquid to enter tosealing device 43. The tube opens the valve when connected but releasesthe valve when removed and allows it to seal the module automatically.The tube has a tee connection, one arm of which is connected to a vacuumpump via a further closable valve. The other arm of the tee connectionconnects via a flexible tube to a container filled with a pre-determinedquantity of the filling liquid. Initially, the container is held at alevel where the liquid is below the level of the filling inlet. The endsof the tube make an airtight seal with the module and containerrespectively. The valve to the vacuum pump is opened and most of the airis pumped out of the module and liquid container. The valve to thevacuum pump is then closed and the container is raised so as to be abovethe level of the filling inlet. Liquid then flows into the module so asto fill the available space to a pre-determined level and immerse thecomponents to be cooled. Finally, the tube with tee connection iswithdrawn from the module and the filling inlet valve sealsautomatically against ingress of air or loss of liquid. The module hasthus been filled with liquid to a predetermined level, leaving a vapouror air space at low pressure, below atmospheric.

An alternative method that is also useful in field filling is to fillwith a cool or warm liquid, since there is increased danger of spillinghot liquid. In this case, an air gap is always left above the liquid toallow for expansion. Liquid may be factory prepared to remove dissolvedgases and is then stored in sealed containers. The interior space of thesealable module 41 is filled with dry air and the sealing device fitted.When filling the sealable module 41 with liquid, the sealing device 43is removed, a specified amount liquid is poured into the sealable module41 via the filling inlet 44 and the sealing device 43 is thenimmediately refitted. The specified amount of liquid added is sufficientfor effective cooling but leaves a remaining space filled with air forexpansion of the liquid at temperatures up to T_(max), the highestenvisaged operating temperature of the system.

At temperatures below the lowest envisaged room temperature, the liquidmay contract further and the electronic circuit board 75 may no longerbe fully immersed in liquid. This is envisaged to occur when the moduleis inactive, in storage or being transported, for example by air, whenlow external pressure and temperature conditions may occur. The seal 62between the housing and cold plate is intended to withstand temperatureand pressure variations between the limits envisaged for inactivity,storage and transportation and the conditions at T_(max).

Above T_(max), the system would be outside its design temperature range.Although higher temperatures are very unlikely, the pressure reliefvalve device 45 allows escape of liquid that has exceeded T_(max), thetemperature at which the liquid fills or is close to filling theavailable space inside the module. The pressure relief device may becombined with the seal 43 for the filling inlet 44.

The first cooling liquid 66 is chosen on the basis of a number ofdesirable characteristics. It should not significantly affect theperformance of the electronic circuit board 75 or the transmission ofinformation between the circuit board 75 and other external devices. Itshould not be corrosive to any component of the cooling module, remainliquid at all operating, storage and transportation temperatures, havesufficiently good specific heat capacity, in order to carry heat awayfrom the electronic components as efficiently as possible, have a highenough coefficient of expansion and low enough viscosity to aid rapidconvection, be low-cost, be safe to use and be non-hazardous in case ofleakage.

One example of a suitable first cooling liquid 66 is a hydrofluoroetherchemical. This has all the desirable characteristics, including a highcoefficient of expansion and sufficiently high specific heat capacity toprovide high mass-flow rate and rapid convection when heated, thuscarrying heat quickly away from the hot components.

In FIG. 3, there is illustrated the cooling unit of FIG. 4, on whichframe 31 is fitted with a cover 33 to form an assembled cooling unit 2.Cooling unit 2 further comprises: first data connector 27; second dataconnector 28; first power connector 29; second power connector 30; andfront panel locking tabs 32.

When housed in a standard equipment rack, each cold plate 60, within itsrespective sealable module 41, is commonly in the vertical plane. Eachcold plate 60 carries liquid from inlet 12 also associated with a pairof sealable modules 41 inside the cooling unit 2.

The cover 33 is held in place by screws 34 or equivalent fixings,protects the sealable modules 41 and other internal parts of the coolingunit 2 and gives additional EMC protection. The cover additionallycompletes an external rectangular box shape that is convenient forsliding into and out of a shelf in a rack for installation, repair orreplacement.

Electrical connections are also made at the rear of the module, forpower 29,30 and data transfer 27, 28. Standard connectors may beemployed to allow connection and disconnection of the module forinstallation and removal.

Reference is now made to FIG. 1, in which there is shown a simplifiedfront view of an equipment rack containing multiple cooling units.Equipment rack 1 comprises: cooling unit 2; additional equipment shelves3; AC power unit 4, which is commonly air-cooled; and cold plate 5 toprovide additional cooling for the AC power unit 4. The AC power unit 4may alternatively be cooled by immersion in a liquid or by thermalcoupling to a cold plate. Rack 1 houses a number of AC power units andcooling modules 2 and has expansion room for further modules inadditional equipment shelves 3. The modules are removable forreplacement or repair. FIG. 1 shows a typical packing density ofmodules. Only one shelf 3 of the rack 1 is filled with cooling units 2.The others could be similarly filled with cooling units 2. Cooling units2 are inserted from the front of the rack.

In FIG. 2, there is shown a simplified cross-sectional side view of theequipment rack shown in FIG. 1. The front 16, side 15 and rear 17 of therack 1 are shown.

The equipment rack 1 additionally houses towards the rear: a firstplenum chamber 18 (a pressure equalisation device); a second plenumchamber 19; a pump 21; a header tank 20; a heat exchanger 22; a firstliquid connector 23; and a second liquid connector 24.

Liquid connections 11 and 12 are also shown on the cooling unit 2. Theseinterconnect with a system of pipes in a second liquid cooling stage ofthe system, which will be described further below. These are normally atthe rear 17 of the rack, although in circumstances where rear access isnot convenient, they could be at the front 16 of the rack. In thisexample, the cooling unit 2 has one liquid inlet and one liquid outlet,serving two independently cooled sealable modules 41 within each coolingunit 2.

The first plenum chamber 18 collects cooling liquid from a number ofcooling units 2. The second plenum chamber 19 distributes cooling liquidto a number of cooling units 2. The pump 21 assists circulation of thecooling liquid via the plenum chambers 18 and 19. The header tank 20 isfor the cooling liquid circulated by the pump 21. The heat exchanger 22transfers heat from liquid in the second liquid cooling stage to liquidin a third liquid cooling stage. Liquid connectors 23 and 24 carryliquid in the third cooling stage to and from the heat exchanger toequipment outside the rack.

Thus, a first stage of cooling electronic components has now beendescribed. The first stage provides a low-cost cooling module, usingnon-forced cooling (in this case using conduction and convection througha cooling liquid to transport heat) and the ability by some means todetach and replace any faulty module with a module that is workingcorrectly. There may be any number from one to a large number of suchmodules in a system.

In the first stage, at least one sealable module 41 is used. Eachsealable module 41 houses one or more electronic circuit boards, powersupply units, DC to DC power converters or disk drives to be cooled.Heat is removed from the heat-generating electronic components to thefirst cooling liquid 66 contained within the sealable module and is thentransmitted from the first cooling liquid 66 via the conduction surface71 to a second cooling liquid flowing through the cold plate base 22.

The second cooling liquid is used in a second stage of cooling and ameans of circulating the cooling liquid is provided so as to carry heataway from the first stage. A third stage of cooling can also be used toavoid the use of liquids flowing through cooling units under highpressure.

Further intermediate stages of heat transfer also use liquid to carryheat to a final heat exchanger. Further cooling stages desirably includecooling liquid flow-rate management for the different stages of thesystem, and pressure management, in order to avoid high cooling liquidpressure in sealable modules, whilst allowing liquid to be pumpedeffectively to a final heat sink. The system thereby uses multiplestages of heat transfer using liquids in all stages up to the final heatexchanger.

Sufficient heat is removed to keep components within their specifiedtemperature range but not significantly more than that. Additional heattransfer and lower temperatures that allow alternative operating modessuch as “over-clocking” of processors are possible using the system butnot necessary in normal operation, since additional energy is consumedin achieving these lower operating temperatures and the alternativemodes of operation are not in common use in large scale systems.

Referring now to FIG. 8, there is shown a schematic view of athree-stage cooling system comprising a single cooling unit 2. Thecooling unit 2 houses two sealable modules 41, each of which has a firstcooling stage 113 using liquid convection and a second cooling stage 114in which second cooling liquid is circulated outside the cooling unit 2.Liquid flow to the two sealable modules 41 is provided via flow splitter55 and liquid flow from the modules 41 is combined in flow combiner 57.The system further comprises: quick release connectors 111; pipes forsecond cooling liquid 112; first pump 116; pump control 117; header tank109; heat exchanger 118; second pump 119; pump control 120; pipes forthird cooling liquid 126; and heat exchanger 121.

Pipes 112 are joined via quick release devices 111 that also contain ameans of isolating the second cooling liquid in the cooling module andpipes. When the cooling unit 2 is connected, the liquid can flownormally but when the cooling unit 2 is disconnected, these close offthe liquid flow and prevent liquid loss from the module or pipes.

The second cooling liquid circulates through the cold plate (not shown)of the sealable module 41 to a heat transfer device 118 and is thenreturned to the cold plate via a header tank 109, which regulates theliquid pressure in the second cooling stage so as to be only moderatelyhigher than atmospheric pressure, and a first pump 116 supplied withelectrical power from pump control 117, which can be varied to alter thepumping rate according to the amount of heat generated in sealablemodules 41 either locally or by means of a control signal from anexternal device. In the illustrated embodiment, the two cooling circuitswithin the cooling unit are connected in parallel via splitter 55 andcombiner 57. The flow-rate in each of the parallel circuits can beseparately pre-adjusted within the splitter 55 and/or combiner 57 totake account of different amounts of heat generated in each arm of thecooling system. The direction of liquid flow is shown by arrows.

The heat transfer device 118 has two liquid flow circuits. The heatedsecond cooling liquid from the cooling module circulates through a firstcircuit. Cool liquid in the third stage circulates through a secondcircuit. Heat is transferred from liquid in the first circuit via aheat-conducting interface to liquid in the second circuit, which thenflows away through pipes 126 to a final heat exchanger 121. Thedirection of liquid flow is again shown by arrows.

Heat exchanger 121 comprises: heat exchanger cooling plate 122; fan 123;and power supply 124. This is a conventional device, commonly referredto as a “dry cooler”, that may use atmospheric air as the final heatsink medium, this being blown by fan 123 driven by electrical power 124across a finned cooling plate or equivalent means of heat transfer tocool the circulating third cooling liquid. The cooled liquid is thenreturned via a pump 119 driven by electrical power 120 to the heattransfer device 118.

The three stages of liquid heat transfer are desirable in situationswhere the final heat exchanger is located some distance from theequipment to be cooled, for example on the roof of a building. In thiscase, the pressure difference between liquid circulating through thefinal heat exchanger 121 and the intermediate heat transfer device 118may be large. The second stage of heat transfer can use a liquid with amuch lower pressure, so that the potential for liquid to leak within thefirst stage cooling modules and damage the electronic circuit boards isgreatly reduced.

Since the second and third cooling liquids are not in contact with theelectronic circuit board 75 (not shown), their characteristics are lessconstrained than those of the first cooling liquid 66. Water, which hasthe highest specific heat capacity of any common liquid and has very lowcost, can be used effectively. An additive to reduce corrosion andbacterial contamination may optionally be used.

The probability of leakage of the second cooling liquid is greatlyreduced by limiting the pressure in the second cooling stage. Headertank 109 provides regulation of the pressure in this stage. If anyleakage should occur, the fluid may be distinguished from liquid used inthe first cooling stage by addition of a small amount of dye. Since thesecond cooling liquid can be water, a range of low-cost non-toxic dyesis available for this purpose.

Referring now to FIG. 9, there is shown a block diagram showing a largerscale three-stage cooling system with multiple cooling units accordingto the invention. Three cooling units, each with two sealable modulesaccording to the invention are shown but, typically, many more units canbe accommodated in a system. This example of a larger scale coolingsystem, comprises: cooling units 130, 131, 132; pipes 129; plenumchamber 147 to combine liquid flow from cooling units; plenum chamber148 to distribute liquid flow to cooling units; pump 134 for secondcooling liquid; header tank 143; heat exchanger 135; pump 136 for thirdcooling liquid; final heat exchanger 137; final coolant entry 138 tofinal heat exchanger; and final coolant exit 139 from final heatexchanger.

A number of cooling units 130, 131, 132 are mounted in a housing or rackwith an arrangement such as that shown in FIG. 1. The liquid flowthrough the cooling units 130, 131 and 132 is connected in parallelfashion via plenum chambers 147 and 148. Each of the cooling units 130,131 and 132 typically contains two or more sealable modules 41 and canbe disconnected and removed from the rack separately, using quickrelease connectors such as those shown in FIG. 8, for replacement orrepair. The number of cooling units can be extended, as indicatedschematically via the additional inputs 141 and outputs 142 of theplenum chambers to a large number.

Plenum chambers 147 and 148 are advantageously insulated to improveefficiency by reducing local heat loss and reducing transfer of heatbetween the input plenum and the output plenum. A further improvement isto locate plenum units directly in line with the connectors of coolingunits 130, 131, 132, thus simplifying pipe arrangements and reducing thetotal number of liquid connectors in a system.

The second cooling liquid flow is divided amongst the cooling modules bya parallel arrangement of pipes 129 from plenum chamber 148, typicallywith one set of pipes per cooling unit, each serving two sealablemodules 41 mounted therein. The flow rate to each sealable module 41 canbe varied by use of restrictors and baffle plates in the quick-connecthydraulic connectors 154.

By adjusting the flow rate to each cooling unit independently, a moreefficient system is produced with a more uniform temperature of theheated second cooling liquid from the various cooling units.

Heated liquid from the cooling units is returned via pipes 129 to plenumchamber 147, where it is combined and delivered via pipes 129 to heatexchanger 135. Cooled liquid from heat exchanger 135 is passed to headertank 143, which regulates the pressure of the second cooling liquid.

Pump 134 drives the circulation of the second cooling liquid by drawingliquid from the header tank and pumping it to plenum chamber 148. Theliquid is then distributed back to the cooling units via pipes 129. Pump134 may be similar to pump 116 of FIG. 8, but is desirably of a largerscale to pump liquid to several cooling units 130, 131, 132 instead ofone. Arrows show the direction of liquid flow. Heat transfer device 135has the same function as the heat transfer device 118 of FIG. 8, exceptthat it is desirably of a larger scale to transfer heat from severalcooling units 130, 131, 132 instead of one.

The third stage of the system uses a third cooling liquid to transferheat from the heat exchange device 135 to a final heat exchanger 137.Pump 136 is used to circulate the liquid. Atmospheric air or coolgroundwater, used as the final heat sink medium, enters the heatexchanger at 138 and leaves at 139. In this case, and especially insystems that cool large arrays of servers, the entropy of the liquidcarrying the heat may be low enough to be used for other purposes,rather than be dumped into the environment. It may be used as a sourceof energy for heating a building for human occupation or the generationof useful amounts of electrical power. In other circumstances, where anunusually high atmospheric temperature would otherwise reduce thetemperature difference between the source and atmospheric final heatsink to too low a level, excess heat may be diverted (by diverting someof the final liquid) to refrigeration (“chiller”) units, or additionalenergy or cost might be expended in the final heat exchanger (such asthe use of adiabatic “dry coolers”, which spray water into the air toreduce the effective ambient temperature, wet bulb temperature).

FIG. 9 also shows signal outputs E1, E2, E3 from cooling units 130, 131and 132. Further signal outputs (not shown) may be provided byadditional cooling units so that the full set is E1,E2,E3 . . . En. Alsoshown are control inputs B and C to pump 134 and pump 135 respectively,and control input D to final heat exchanger 137. These can be used formonitoring and control purposes. This will be explained in more detailbelow.

Referring now to FIG. 10, there is shown a monitoring and control system140 for use with the three-stage cooling system of FIG. 9. The systemcomprises: data inputs 146; and pump control outputs 145.

A monitoring and control system is used to monitor the temperatures ofthe electronic devices to be cooled and to adjust the flow rate of thesecond cooling liquid, third cooling liquid or both to provide optimumcooling. Sensors on each electrical circuit board measure thetemperature of the electronic components and convert this information toanalogue or digital signals. FIG. 9 shows signal outputs E1, E2, E3,which can be extended to En, where n is the total number of coolingunits that contain temperature-sensing devices, and where each signalcontains information about the temperature of the one or more sealablemodules in each cooling unit. These outputs are sent to the controlsystem 140.

The control system 140 computes the optimum flow rate of second coolingliquid, the optimum flow rate of the third cooling liquid and the rateat which the final heat exchanger should operate and produces inresponse a control message B, C, D. Control messages B and C are used toturn on or off or vary the pumping rate of pumps 134 and 136respectively. In addition, the control system determines whether or notthe final heat exchanger needs to adjust its cooling rate, for exampleby altering the flow level of the final heat sink liquid or air, usingcontrol signal D.

The overall thermal capacity of the system is large, so that short termrelatively large increases in ambient temperature (and thus thetemperature of the final heat sink) can be accommodated without the keycomponents exceeding their maximum temperature ratings. The ambienttemperature on the hottest days may rise to a level where not all of theheat generated by the components to be cooled can be removed. Theoperating temperature of components may rise but the high thermalcapacity means that the rise takes place slowly and maximum temperaturesare not exceeded. During the cooler part of the diurnal cycle, more heatcan be removed than is generated. In this way the system can be operatedat locations with climates that would not otherwise allowrefrigeration-free cooling. The control system can be optimised to useambient temperature data, measured from external sensors and fromhistorical trend data and statistics, to ensure that the flow rates areoptimised. In the rare event that very exceptional temperatures occur,timely warning can be given to either reduce the effective temperatureof the final heat sink (such as by switching to an active mode ofcooling) or otherwise enable the system operator to take appropriateremedial actions.

In systems where “run-time hardware abstraction” of processing systemsis used (such as with “virtualisation” or “run-time middleware”), themonitoring and control system is particularly important. In systems withhardware abstraction, the multiple electronic circuits boards(“hardware”) and multiple computer operating systems are not in one toone correspondence. When one circuit board is under high processingload, some activity can be shared with other boards. Processing isdistributed across the items of hardware. As a result, heat generated indifferent parts of the systems varies from time to time. Cooling ratesin different parts of the system may then be adjusted dynamically toalign with the changes in amounts of heat generated.

If the first cooling liquid in the sealable module 41 (and thus, thecircuit board 75) is to operate at a desired temperature, T_(case), andthe final heat sink is at a known temperature T_(hs), this defines thetemperature difference that the cooling system desirably provides, inthat ΔT=T_(case)−T_(hs). Since T_(case) is desirably restricted to nohigher than the maximum operating temperature of the circuit board,T_(case,max), then ΔT≦T_(case,max)−T_(hs).

Semiconductor manufacturers are increasingly reducing the maximumoperating temperature of their processors. This reduces the temperaturedifference, particularly when refrigeration is not employed to increasethe local temperature difference. A further difficulty arises when thefinal heat sink is at atmospheric temperature, which may be as high as40 degrees centigrade.

Reducing the thermal resistances in the system can assist to achieve thedesired temperature difference. Systems which transfer heat throughfluid flow may result in reduced thermal resistance compared withsystems which transfer heat, either in full or in significant part,through static, thermally-coupled bodies or through gases. For example,the flow rate of the second cooling liquid can be adjusted to reduce thethermal resistance between the sealable module 41 and the heat exchanger118. Additionally or alternatively, the area of contact between thesecond cooling liquid flowing through the channels 61 and the conductionsurface 71 can be varied to affect the thermal resistance.

The use of tightly-packed channels 61 increases the pressure drop (i.e.hydraulic pressure losses) in the cold plate which increases the pumpingcosts for the secondary cooling liquid circuit. The width of the channelcan be modified to reduce pressure losses and decrease the effect of theconduction surface 71 in the cold plate 22 in transferring heat intowater channels.

At one extreme, the channels 61 could be as wide or wider than thedimensions of the housing 81 to present a “flood plain”, rather than a“serpentine river”, of second cooling liquid. However, controlling flowof second cooling liquid in such an embodiment may be difficult andfeatures such as eddy currents may cause local build up of heat, whichis undesirable as it will reduce rate of heat transfer for adjoiningareas of conduction surface 71.

Therefore, the channel 61 width can be less than, but significant incomparison with a dimension of the housing 81. Optimisation of thecross-section of the channels 61 can improve the temperature difference.Channels 61 that are approximately 20% of the length of the longestchannel 61 may be defined by baffles that direct flow over specificareas. Also, the flow of the second cooling liquid can be portioned withthe channels 61 into sections such that the water is distributed intozones and slowed over areas with greatest heat flux (e.g. processors),the reintroduction of heat back into the primary coolant can beminimised, whilst the entropy of the extracted heat can be minimised.

Whilst a preferred embodiment and operating modes of the presentinvention have been described above, the skilled person will appreciatethat various modifications can be made.

For example, cold plate 5 shown in FIG. 1 is optional and the skilledperson will appreciate that this need not be included. Instead ofinserting cooling units 2 into the equipment rack 1 from the front, theycould be inserted from the rear of the rack. Advantageously, the coolingunits could be adapted to carry only one sealable module in each unit,so that units may then be inserted both at the front and rear of therack. Electrical and liquid connections are then made in the middle ofthe rack. A single module unit is much lighter in weight than a twomodule unit and can be safely carried, fitted or removed by a singleperson.

Although intermediate stages of heat transfer and a final heat sink mayuse liquid cooling, other cooling mechanisms can alternatively be used,such as convection cooling.

The skilled person will also recognise that the present invention can beimplemented and operated in a number of different ways. Referring now toFIG. 11A and FIG. 11B, there are shown side views of a second embodimentof a sealable module 150 according to the present invention, which is analternative to that described above. The sealable module 150 comprisesan outer cover 151 and housing 152. Although the second embodimentdiffers slightly from the first embodiment, the skilled person willappreciate that many features of the two embodiments areinterchangeable.

The channels in the cold plate 60 are closed by the outer cover 151. Theassembly, which defines the channels, can be termed a “water jacket”,because it dictates the flow of water (as second cooling liquid) forheat to flow over a heat transfer surface, such as a conduction surface71.

Referring now to FIG. 11C, there is shown a more detailed view of thesealable module according to FIG. 11A and FIG. 11B. The sealable module150 also comprises a heat transfer surface 153, which together with theouter housing 152 defines channels 156. Also, the heat transfer surface153 and lid 152 (which can be termed a base or housing) define an innerchamber with an internal volume for locating the electronic device 155to be cooled and the first cooling liquid (not shown). Connectors 154are also shown, for allowing flow of the second cooling liquid throughchannels 156.

This alternative embodiment of a module may therefore comprise an innerhousing, containing the first cooling liquid and one or moremotherboards, substantially sealed (except for a filling port). A heattransfer surface 153 has a gasketed interface with the inner housing andfins facing into the first cooling liquid, shaped to match the profileof the at least one motherboard. The outer housing 152 also has agasketed interface with the heat transfer surface 153, and contains atleast one secondary cooling liquid circuit channel 156, formed withbaffles on the heat transfer surface 153 or on the interior surface ofthe outer housing 152. The at least one channel 156 is optimised todirect the second cooling liquid appropriately over the heat transfersurface 153 with minimised pressure loss. The outer housing 152 hasquick-connect hydraulic connectors 154 to enable the channel 156 to beconnected to the inlet and the outlet of a rack second cooling liquidsupply.

This design allows much tighter integration between the inner housing,heat transfer surface 153 and outer housing 152 potentially to make asmaller unit, which may allow increased packing density of modules. Finsor baffles may be provided on both sides of heat transfer surface 153.These can, for example, provide additional flow control of secondcooling liquid and increase surface area for conduction.

The materials for the present invention can be varied. Metal materialsare good conductors, but expensive. Also, if the heat transfer surface153 or conduction surface 71 (which can be similar or identical) aremade of metal and are large, they may be more likely to warp, puttingstress on seals, especially if multiple sealable modules are mountedthereon, meaning areas of potentially different temperature.

In contrast, synthetic plastic materials are inferior conductors incomparison with metal. Known thermally conductive plastics typicallyconduct 20 W/mK compared to 141 W/mK for aluminium. Higher performancethermally conductive plastics are also usually electrically conductive,which is not a desirable characteristic. However, these materials areless expensive, of lighter weight and are less likely to corrode in thepresence of hot water (notwithstanding the possible addition ofcorrosion inhibitors to the second cooling liquid) than metals.

Optimisation of the temperature difference by control of second coolingliquid flow rates, area of heat transfer and channel cross-section canallow the use of plastic without significant reduction in thetemperature difference. In particular, plastic can be used for the basepart 22 of the cold plate or the outer housing (“water jacket”)described above. A plastic material reduces the amount of heattransferred through the outer wall of the base part 22 or outer housing152 and into the local ambient environment, reducing heat lost in thisway and increasing efficiency of heat removal into second coolingliquid.

Additionally or alternatively, the conduction surface 71 or heattransfer surface 153 can be made of plastic. This may provide additionalexpansion capacity for the first cooling liquid within the sealedhousing. Such a material might be co-moulded with a rigid centralthermal conductive plastic and peripheral ring of flexiblenon-conductive plastic.

A number of features of the embodiment described above will beunderstood as optional to the skilled person and might be omitted. Thesemay include insulation 73, which could additionally be made of a fireretardant material and quick release connectors 111. Also, the skilledperson will understand that alternative constructions for the cold plate60 or outer housing 152 can be used and that the projections 96, 97 canbe of different length and cross-section to that described.

Although an embodiment described above uses a cooling unit 2 in whichone sealable module 41 is affixed to a cold plate 60, it will berecognised that two or more sealable modules 41 might be coupled to acommon cold plate. Also, cooling units 2 may be inserted from both backand front of the rack.

The electronic circuit board can be combined with housing 81 to form anintegrated assembly. This provides a means of connection to electroniccomponents directly from the circuit board, thus reducing the risk ofliquid leaking from cable seals in the module, reducing the overallwidth of a sealable module and increasing packing density of coolingunits within a rack.

The data transmission cables 46 can be replaced by fibre optic cables,optical or infra-red ports or wireless connection between the electroniccircuit board and the exterior of the sealable module. Power supplyconnections would normally be wired, even when the data transmission isby other means, although alternative power supplies may be employed,whilst avoiding fluid leakage.

The second cooling liquid may be distributed via pipes with individualflow control valves, rather than a plenum chamber. The valves may belocally adjusted or controlled automatically by a central monitoring andcontrol system similar to control system 140 shown in FIG. 10 inresponse to temperature and status information from the componentshoused within the sealable modules 41. Also, in the system of FIG. 8,heat exchanger 121 can alternatively be replaced by cool groundwater ora number of configurations including bypass circuits to transfer someheat to refrigeration systems. To provide resilience and redundancyadditional “back-up” pumps and circuits may optionally be provided.

When the final heat sink 121 is close to the equipment to be cooled andthe pressure of the cooling liquid circulating in this stage can belower, a second stage of cooling might be omitted. In this case, thesecond cooling liquid circulates directly through the final heatexchanger. Pump 116 and intermediate heat transfer device 118 or 135 areomitted. As with the embodiment illustrated in FIG. 8, the three-stagesystem shown in FIG. 9 could be reduced to two stages if the liquidpressure in the final stage were low enough.

What is claimed:
 1. A cooled electronic system, comprising: a sealedcontainer comprising: a housing; an electronic device; and a firstcooling liquid; a first heat transfer device defining a first channelfor receiving a second cooling liquid, the first heat transfer devicebeing configured to transfer heat between the first cooling liquid andthe first channel through at least a portion of a conduction surface;and a piping arrangement, configured to transfer the second coolingliquid to and from the first heat transfer device; wherein the system isconfigured to set one or both of: the flow rate of the second coolingliquid through the first channel; and the portion of the conductionsurface through which heat is transferred to the second cooling liquid,such that the temperature of the electronic device is controlled so asnot to exceed a predetermined maximum operating temperature and whereinthe first cooling liquid remains in a state at least consistingessentially of a liquid state; and wherein at least a portion of theconduction surface or housing is shaped in conformity with the shape ofthe electronic device.
 2. The cooled electronic system of claim 1,wherein the conduction surface has at least one projection for receivingheat from the first cooling liquid.
 3. The cooled electronic system ofclaim 2, wherein the at least one projection is arranged in conformitywith the shape of the electronic device.
 4. The cooled electronic systemof claim 3, further comprising a component heat sink coupled to theelectronic device and comprising at least one projection arranged tocooperate with the at least one projection of the conduction surface. 5.The cooled electronic system of claim 2, wherein the at least oneprojection comprises a fin arrangement.
 6. The cooled electronic systemof claim 2, wherein the at least one projection comprises a pinarrangement.
 7. The cooled electronic system of claim 1, furthercomprising a flow control device, arranged to control the flow rate ofthe second cooling liquid, such that the temperature of the electronicdevice does not exceed a predetermined maximum operating temperature. 8.The cooled electronic system of claim 1, wherein the sealed container isa first sealed container, and further comprising: a second sealedcontainer comprising: a second housing; a second electronic device; afourth cooling liquid for receiving heat from the second electroniccomponent; and a third heat transfer device comprising a fourth channelfor receiving a fifth cooling liquid, the third heat transfer devicebeing configured to transfer heat from the fourth cooling liquid to thefourth channel.
 9. The cooled electronic system of claim 8, wherein thefirst channel and the fourth channel are coupled to combine the secondcooling liquid and the fifth cooling liquid.
 10. The cooled electronicsystem of claim 9, further comprising a plenum chamber, arranged tocollect the combined second cooling liquid and fifth cooling liquid. 11.The cooled electronic system of claim 9, further comprising a flowcontrol device, arranged to control the flow rate of the combined secondcooling liquid and fifth cooling liquid, such that the temperatures ofthe first electronic device and the second electronic device do notexceed first and second predetermined maximum operating temperaturesrespectively.
 12. The cooled electronic system of claim 11, wherein theflow control device comprises a flow diverting arrangement, the flowdiverting arrangement being configured to set the flow rate of thesecond cooling liquid such that the temperature of the first electronicdevice does not exceed a first predetermined maximum operatingtemperature, and to set the flow rate of the fifth cooling liquid suchthat the temperature of the second electronic device does not exceed asecond predetermined maximum operating temperature.
 13. The cooledelectronic system of claim 8, further comprising a fourth heat transferdevice comprising a fifth channel for receiving the fifth cooling liquidfrom the fourth channel, and a sixth channel for receiving a sixthcooling liquid for coupling to a heat sink, the second heat transferdevice being configured to transfer heat between the fifth channel andthe sixth channel.
 14. A method of cooling an electronic device,comprising: operating the electronic device within a container, thecontainer also comprising a first cooling liquid, such that heatgenerated by the electronic device is transferred to the first coolingliquid, the container being sealed to prevent leakage of the firstcooling liquid; transferring heat between the first cooling liquid and asecond cooling liquid in a first heat transfer device; piping the secondcooling liquid from the first heat transfer device to a second heattransfer device; and transferring heat between the second cooling liquidand a third cooling liquid in the second heat transfer device; andpiping the third cooling liquid to a heat sink; wherein the firstcooling liquid remains in a state at least consisting essentially of aliquid state during operation of the electronic device.
 15. The methodof claim 14, wherein the step of transferring heat between the firstcooling liquid and the second cooling liquid is carried out byconduction.
 16. The method of claim 14, further comprising: controllingthe flow rate of the second cooling liquid, such that the temperature ofthe electronic device does not exceed a predetermined maximum operatingtemperature.
 17. The method of claim 14, further comprising: controllingthe flow rate of the third cooling liquid, such that the temperature ofthe electronic device does not exceed a predetermined maximum operatingtemperature.
 18. The method of claim 14, wherein the first heat transferdevice comprises a conduction surface, further comprising: setting theportion of the conduction surface through which heat is transferred tothe second cooling liquid, such that the temperature of the electronicdevice is controlled so as not to exceed a predetermined maximumoperating temperature.
 19. The method of claim 14, further comprising:controlling at least one of: the flow rate of the second cooling liquid;and the flow rate of the third cooling liquid, such that the temperatureof the electronic device does not exceed a predetermined maximumoperating temperature and such that, during a first time period, theheat transfer rate between the second cooling liquid and the thirdcooling liquid or between the third cooling liquid and the heat sinkdoes not go above a predetermined maximum rate, and such that during asecond, later time period, the heat transfer rate between the secondcooling liquid and the third cooling liquid or between the third coolingliquid and the heat sink may go above the predetermined maximum rate.20. A method of cooling an electronic system, comprising: carrying outthe method steps of cooling an electronic device in accordance withclaim 14; operating a second electronic device within a secondcontainer, the second container also comprising a fourth cooling liquid,such that heat generated by the second electronic device is transferredto the fourth cooling liquid, the second container being sealed toprevent leakage of the fourth cooling liquid; and transferring heatbetween the fourth cooling liquid and a fifth cooling liquid in a thirdheat transfer device.
 21. The method of claim 20, further comprising:combining the second cooling liquid and the fifth cooling liquid. 22.The method of claim 21, further comprising: piping the second coolingliquid from the first heat transfer device and the fifth cooling liquidfrom the third heat transfer device to a plenum chamber.
 23. The methodof claim 21, further comprising: controlling the flow rate of thecombined second cooling liquid and fifth cooling liquid, such that thetemperature of the first electronic device does not exceed a firstpredetermined maximum operating temperature and such that thetemperature of the second electronic device does not exceed a secondpredetermined maximum operating temperature.
 24. The method of claim 20,further comprising: piping the fifth cooling liquid from the third heattransfer device to a fourth heat transfer device; and transferring heatbetween the fifth cooling liquid and the third cooling liquid in thefourth heat transfer device.
 25. A method of cooling an electronicdevice, comprising: operating the electronic device within a container,the container also comprising a first cooling liquid, such that heatgenerated by the electronic device is transferred to the first coolingliquid, the container being sealed to prevent leakage of the firstcooling liquid; transferring heat between the first cooling liquid and asecond cooling liquid in a first heat transfer device; transferring heatbetween the second cooling liquid and a heat sink; and controlling theheat transfer rate between the second cooling liquid and the heat sink,such that the temperature of the electronic device does not exceed apredetermined maximum operating temperature and such that, during afirst time period, the heat transfer rate does not go above apredetermined maximum rate, and such that during a second, later timeperiod, the heat transfer rate may go above the predetermined maximumrate.
 26. A cooled electronic system, comprising: a sealed containercomprising: a housing; an electronic device; and a first cooling liquid;a first heat transfer device defining a first channel for receiving asecond cooling liquid, the first heat transfer device being configuredto transfer heat between the first cooling liquid and the first channel;and a second heat transfer device comprising a second channel forreceiving the second cooling liquid from the first channel, and a thirdchannel for receiving a third cooling liquid for coupling to a heatsink, the second heat transfer device being configured to transfer heatbetween the second channel and the third channel.
 27. The cooledelectronic system of claim 26, wherein the first heat transfer devicecomprises a conduction surface, the housing and the conduction surfacetogether defining a volume in which the electronic device and the firstcooling liquid are located.
 28. The cooled electronic system of claim27, wherein the conduction surface separates the volume and the firstchannel to allow conduction of heat between the volume and the channelthrough the conduction surface.
 29. The cooled electronic system ofclaim 28, wherein at least a portion of the conduction surface orhousing is shaped in conformity with the shape of the electronic device.30. The cooled electronic system of claim 27, wherein the conductionsurface has at least one projection for receiving heat from the firstcooling liquid.
 31. The cooled electronic system of claim 30, whereinthe at least one projection is arranged in conformity with the shape ofthe electronic device.
 32. The cooled electronic system of claim 31,further comprising a component heat sink coupled to the electronicdevice and comprising at least one projection arranged to cooperate withthe at least one projection of the conduction surface.
 33. The cooledelectronic system of claim 30, wherein the at least one projectioncomprises a fin arrangement.
 34. The cooled electronic system of claim30, wherein the at least one projection comprises a pin arrangement. 35.The cooled electronic system of claim 26, further comprising a flowcontrol device, arranged to control the flow rate of the second coolingliquid, such that the temperature of the electronic device does notexceed a predetermined maximum operating temperature.
 36. The cooledelectronic system of claim 26, further comprising a flow control device,arranged to control the flow rate of the third cooling liquid, such thatthe temperature of the electronic device does not exceed a predeterminedmaximum operating temperature.
 37. The cooled electronic system of claim26, wherein the sealed container is a first sealed container, andfurther comprising: a second sealed container comprising: a secondhousing; a second electronic device; a fourth cooling liquid forreceiving heat from the second electronic component; and a third heattransfer device comprising a fourth channel for receiving a fifthcooling liquid, the third heat transfer device being configured totransfer heat from the fourth cooling liquid to the fourth channel. 38.The cooled electronic system of claim 37, wherein the first channel andthe fourth channel are coupled to combine the second cooling liquid andthe fifth cooling liquid.
 39. The cooled electronic system of claim 38,further comprising a plenum chamber, arranged to collect the combinedsecond cooling liquid and fifth cooling liquid.
 40. The cooledelectronic system of claim 38, further comprising a flow control device,arranged to control the flow rate of the combined second cooling liquidand fifth cooling liquid, such that the temperatures of the firstelectronic device and the second electronic device do not exceed firstand second predetermined maximum operating temperatures respectively.41. The cooled electronic system of claim 40, wherein the flow controldevice comprises a flow diverting arrangement, the flow divertingarrangement being configured to set the flow rate of the second coolingliquid such that the temperature of the first electronic device does notexceed a first predetermined maximum operating temperature, and to setthe flow rate of the fifth cooling liquid such that the temperature ofthe second electronic device does not exceed a second predeterminedmaximum operating temperature.
 42. The cooled electronic system of claim37, further comprising a fourth heat transfer device comprising a fifthchannel for receiving the fifth cooling liquid from the fourth channel,and a sixth channel for receiving a sixth cooling liquid for coupling toa heat sink, the second heat transfer device being configured totransfer heat between the fifth channel and the sixth channel.